Alignment of optical sources, such as a laser or a light emitting diode, to optical waveguides requires accurate alignment of the optical source with the waveguide. The sizes of the active region of an optical source and the core of the waveguide to be aligned are often very small, on the order of micrometers (□m). A coupling element, such as a lens, is typically used to focus the diverging optical rays of an optical source into the core of the waveguide.
Active alignment is required to achieve reasonable coupling efficiency between the optical source and the waveguide. During active alignment, components are moved relative to each other to find the optimal position. The optical source emits light and an intermediate lens focuses the emitted light onto the core of a waveguide. Light coupled into the core of the waveguide is emitted from the opposite end of the waveguide, where it is measured by a photodetector. As the optical source, the lens and the waveguide are moved laterally, axially, and angularly with respect to each other, the light transmitted through the waveguide is monitored for peak output intensity. Active alignment of three components is time consuming and labor intensive, increases manufacturing time and cost, and increases product prices.
Permanently securing the components in their relative positions after alignment also causes problems. For a solid state laser aligned with a single mode optical fiber, the movement of the aligned components must be less than about 500 nm. Adhesives, such as epoxy, shrink during curing, so that the aligned components are moved as the epoxy cures. Component offsets of one micrometer or more commonly occur. One approach to overcome this problem is to continue active alignment as the epoxy cures. This requires a series of labor intensive partial-curing and aligning steps, further increasing manufacturing complexity, time and expense.
Clamps can be used to mechanically secure the components, but stress from the clamps shifts the relative position of the components. Component offsets of one micrometer or more commonly occur. Although the components can be mounted with an offset to allow for the movement from clamping, the additional uncertainty results in many unsuccessful alignments.
It would be desirable to have an optical coupler that that would overcome the above disadvantages.